Well, there are a number of factors, but let's start with this one. Suppose you just intend to drive and have no ambition of hot-rodding it or anything like that. Then it comes down to dollars and cents, and you'll be deciding between 2.0 gas and the TDI. (No point going 1.8T or VR6 if performance is a secondary factor.).
How much do you plan to drive each year? Given that, figure out how much fuel you are going to use each year (you can use the EPA or Transport Canada combined highway and city consumption estimates as a good guide). Multiply that by the current cost of each type of fuel in your area. You're going to find that the TDI costs about half as much in fuel to keep going. Depending on how much you drive, this could be a significant amount. (In my case, it's about C$120 per month.)
Maintenance costs are about the same whichever way you go.
The TDI costs more to buy. You could just divide the extra purchase cost by the annual savings to get a break-even period, but that would be too simplistic. In my area, used diesel VW's are worth more than used gas VW's, generally by more than the extra cost of the TDI engine in the first place ... which really means the break-even period is nil. (I paid a C$3000 premium for a used TDI over a similar VR6 with about 100,000 km, and it still made sense.)
Do you plan to keep the car for a long time? Advantage TDI. I drive my vehicles into the ground.
Suppose that performance is a factor but so is operating cost. Advantage TDI. Stock, it's about like a 2.0, but chipped it's more like either a 1.8T or a VR6. Advantage: TDI.
Suppose performance is the only factor and operating cost means nothing. Advantage: I'd say 1.8T.
Hope this helps. You owe it to yourself to take a few test drives in different models to see what you think of each.
For me, it took one test-drive in a Jetta TDI to get hooked.
Brian P.
'96 Passat TDI
Thanks.